Polling will always increase device load in the absence of data versus
Basically, the system must spend time checking each potential polled
data source over and over again. This creates load in the form of IO
wait time and fills up queues with extra instructions that do not exist
in an Interrupt driven implementation. The term "Load" should not be
confused with a CPU that is continually filling it's various caches and
whatnot, as is the case with number crunching tasks like high data rate
VPN tunnels and deep content packet rewrites.
Polling should be applied when you have at least a semi constant stream
of traffic. Basically, the CPU doesn't need to be told something that
it already knows - the network card wants to spew packets onto a bus of
All CPUs can benefit from the polling approach as opposed to an
Interrupt driven mechanism, and likewise all CPUs can be hindered by it.
Most benefit from my experience, but I haven't exactly gone and
tested it on every system that I've built - I usually just enable it
Some polling implementations utilize a hybrid approach, wherein only
received traffic is handled via polling and transmitted traffic is
handled via Interrupt. It depends on the driver and the chipset of the
NIC as to which method of polling, if any, is supported.
Of course, neither method works if you have just too much bandwidth for
the box to handle.
As Craig says, YMMV.
Craig FALCONER wrote:
> Beg to differ - I have a nokia IP330 with a P166 CPU.
> Turning on polling increased the machine's load to a noticeable level.
> So its really "YMMV" but slower CPUs may not benefit from that.
> -----Original Message-----
> From: Steve Thomas [mailto:sthomas at consultant dot com]
> Sent: Friday, 9 February 2007 9:58 a.m.
> To: Lonnie Abelbeck; m0n0wall List
> Subject: Re: [m0n0wall] Hardware suggestion
> Good thought, I don't really know. AFAIK, turning on polling generally
> improves performanceover having it turned off.
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